Feed system for grinding mills



May 4, 1943. w. c. HANNA Erm.

2,318,306 FEED SYSTEM FOR GRINDING' MILLS 'Y v Filed Nov. 25, 1941 hm/Mira@ SIP/vpn@ www? 60,9962" Efo ves siek 3%* 211,--- '7 fraafQ/Poz n /w A1 3 P//xzn//VG- /\7/.

Wgr/yal? Mln/fr Patented May 4, 1943 e 2,318,396- rEED SYSTEM FOR GRINDING MILLS- WilsonC. Hanna, Harry E. Kaiser, and Arthur Harvey, Colton', Calif., assig'nors to California Portland Cement Company, Los` Angeles, Calif.,

a corporation ol California l f f f rnisinvention has to do generauy with Vfeed control for grinding mills in the operation ofr which solid granular or lumpy material is `fedV f for grinding, the ground material is separated l into' relatively line and coarse particles, and the v latter circulated for regrinding in the mill. While the invention is broadly applicable Vto various dry grinding operations of this general character, it

has been applied with outstanding success in grinding Portland cement materials, includingY Y raw (argillaceous and calcareous) materials as well as thel cement clinker. `Accordingly,lthe invention will be described typically'with reference to grinding operations'in the manufacture of Portland cement. A

Ordinarily, and as herein contemplated, a grinding mill, for example a'rotary ball millof given size and ball load, and rotating at constant speed, will. apply to the material undergoing grinding what may be termed constant grinding energy. It is of course desirable in most instances that the fineness of the ground product be as constantly uniform as possible, and theoretically p such uniformity would exist where the material fed to the mill has uniform size, composition, and rate of delivery. In practice, however, any or all of these conditions are subject to variation, and consequently it becomes necessary to Ymaintain the grinding operation under a control tending to prevent or minimize changes in the line-V ness of the product. Since itis impossible or impractical to obtain this resultby varying the. composition or size of the material being ground, the customary practice has been to regulate the rate at which the material is fed to the mill.

Heretofore, this has been done manually or by automatic feed controls, the latter .involving considerable expense and mechanical complications, and oftentimes failing to maintain the desired accuracy of control over the fineness of the final product. 'I'he'primary object of this' invention is to provide an automatic and exceptionally accurateieed control of such extreme simplicity, both mechanically and in its operation, that the usual feed control mechanisms -may be entirely dispensed with in favor of a simple arrangement for merging the mill feed and recirculated particle streams under conditions such that the former is controlled by the latter and the mill is caused to deliver a, product of uniform i'lneness. The invention is predicated upon the observa` ration, as by entrainment 'in' an air stream, into" relatively finelparticles -which constitute the` ground product, and relatively coarse particles or rejects which are recirculatedinj a stream of mill. Preferably thelatter stream is e Application November V25,v 1941,;se'ria1 No. 420,384 Y 15 claims'. (c1. :i3- 44V mill can be made to vary in vinverse proportion to the quantity of recirculated particles, by sim 'A ple and directiimpingem'ent of thetwo streams.

Thus, the entire mechanical requirements of the' system maybe satisfied merely by mergingthe streams in a manner such that a decrease in the rate of recirculation of the separated coarse particles Will cause a compensating increase in the rate of the mill feed, and conversely as the recirculated particle flow increases.

VAccording to the illustrative system hereinafter 'l'.

describedfin detail, the grinding mill receives a continuous gravity feed ofthe coarsev material to be ground, and which may consist of Portland cement raw materials,A or Portland cement clinker as it is produced from the calcining kiln. From the grinding. mill, the material is taken for sepaair to the main feed stream gravitating into thev caused. to pass through an opening of particular shape, as later described, and the reject stream a manner whereby the Vmain feed rate is Vsubject to variation or control in inverse relation to the quantity rate of 'recirculation of=` the coarse parti-` cles rejected bythe separator.

'I'he invention contemplates various particular features such as the use of interchangeableconi trol gates havingdifferent size openings tofvary correspondingly theA rate at whichthe main stream of coarse material is .fed to the mill, and the provision ofY means whereby the angle Vof impingement of the recirculated and main feed streamsmay be var-led to sensitize vor 'otherwise desirably affect the control. All suchy features, as well as the broader aspects .and objects of the invention, will be'understoodto better advantage from the detailed description to fol1ow.\ Reference is had `\throughout the description to the accompanying drawing, in which:

Fig. 1 illustrates diagrammatically a typical Y feed control system embodying the inventionf tion that an increase in the recirculation rate of Y Y the separated coarse particles results from the millgrinding coarser, and the discovery that the rate at which the raw material is fed to the Fig. 2 is an enlarged sectionalr view taken at Ju Fig. 3 is a fragmentary Section taken on line f from the. separator is projected against' the main feed stream at theroutlet side of the opening, all in f generally indicated at I 2, and thence through passage I3- into the conventionally illustrated grinding mill I4. The latter of course may be of any suitable type and constructiomoperating to apply to the material owing through. the

mill', constant or uniform grinding energy. Typically, the grinding may be accomplished by a ball mill rotating at constant speed.

The ground material is discharged from the mill through outlet passagev I5 and then taken 'i for separation into relatively fine and coarse particles. As illustrative, the grinding mill discharge may be transferred within conduit I6 by a conveyor or other suitabler means and introduced into a separator I8 (for example, the commonly used Sturtevant rotary blower type" separatorwithin whichV air flow is gen'erate`d-f`jr.A classifl-VV` cation of the particles to be separated), from thebottom 'of which the fines, i. e. the materials that are ground to the desired neness, arwithdrawn through line I9. Relatively coarse par. ticles which have not been reduced in the grinding mill to the desired flneness, .are rejected by the separator: and recirculated in an airstream' developed .by the` separator, through conduit 2U to the feed controly I2, whereinthe coarse rejects are combinedwith the main feed stream, as will Y nowV appear.

Referring to.Fig. -2, the juncture of passages II, I3, and,.20 Yls formed by a'box 2IA accessible through topV opening 22 .normally'closedby a cover 23; The box.-2.lpcontains a verticallypositioned feed gate 24 extending transversely the distance between-the side walls of the box and confined between suitable guides 25. The lower the lmethod thatincludes projecting a stream of stream, the separator vrejects strike the main feed` stream with suilicient forcel to control, at least within necessary limits. the rate at which the material .is discharged through opening 21.

, Thus as the percentage of rejects increases, thev increased force ofthe projected reject stream exerts a retarding effect upon the rate at which the main feed stream passes through opening 21 to the grinding. mill, and conversely as the percentage of rejects decreases and the force of the projected reject particles against the main feed stream diminishes. Consequently, if the mill for any reason starts to grindcoarsef the 'immediate result will be a decrease in the rate of mill feed, continuing until the ground material again-reaches a predetermined degree of flneness. And where such desired neness is being exceedjed, the consequent increase in the mill feed rate the separated coarse particles in varying quantities against said stream of solid' material in a direction and at a velocity such that the kinetic energy of said particles variably restrains the flow of said solid' material to the mill, thereby causend ofthe controlgate rests at 26: on the bot-.-

ltomsurface of the inclined feed passage II.-v

As `best killustrated in Fig. 3, the main-feed stream discharges from passage II into the vertical passage ll3, through aniopening 21.inthe feed gate, this .opening being smallerthan the cross-sectional'area of passage II and therefore restricting to some extent the passage of material' at the location ofthe gate.. The degree ofrestriction is Yvariable by substitutingfeed gates havingadiiferent size-openings. After con--V siderable experimentation and test. operations, best resultswith respect to uniformity of control have been .obtained by using aA form of opening 21 of downwardly increasing width,'so that'.

somewhat greaterrestriction .is given to the materialpassing through the upper portion of thev opening and in the general vlocation of the impingement of the recirculatedreiect stream. It is preferred to forrnthe opening21 as as isosceles trapezoid, theproportions of which With relation .to passage II are substantially as illustrated l inFig. 3. y

Referring again to Fig.. 2,.V passages 20and II are arranged so thattheir longitudinal axes, or the lines of flow of. the materials through them, are disposed at substantially a 9 0 degree angle. Passage 20, however, is relatively'elevated, so that the material discharged therefrom impinges at 28- against the main feed stream more directly opposite the centralv portion of the feed gate opening 21. This angle of impingement maybe varied by changing theangularity of the outlet end of passage 20. 'For-example, the discharge end of the-passagemay be Yformed as a chute 30 pivotally supported at 3I. and adjustable about the pivot to vary its angularity, by set screw 32 or other suitable means. Y I

Being projected in the air stream at consid erable velocity at 28 :against the main feed ing the'rate at which `saidmaterial is fed to the mill to decrease as the quantity of separated coarse particles being projected against said stream of material increases, and to increase as said quantity of the separated coarse particles decreases.

2. In Ythe operation of a grinding mill to which a stream of solid material flows for grinding and from which theground material is taken for sep-Y aration into relatively fine and coarse particles;A

the method that includes projecting a stream comprising substantially all of the separated coarse particles in varying quantities against said stream of solid material in .a direction and at a velocity such thatV the kinetic energy of said particles ,variably restrains the ow of said solid material. to the mill, thereby causing the rate at which said material is fed to the mill to decrease as the quantity of separated coarse particles be-` ing projected against' said stream of material increases, and to increase as saidquantity of the separated coarse particles decreases.

3. In'the operation of a grinding mill to which a Ystream of solid material is fed for grinding andfrom which the ground material is takenv for separation into relatively ne and coarse particles; the methodethat includesV maintaining a gravity .feed of a downwardly flowing stream of' said' solid material into `the mill, and controlling the'rate of said feedby projecting astream of stream of material increases, and t0 increase asr the separated coarse particles in varying quantitles against said`stream of solid material in a direction and at a velocity such that the kinetic energy of said particles variably restrains the flow of said solid material to the mill, thereby causing the rate at which said material is fed to the mill toY decrease as the quantity of separated coarse particles beingv Vprojected against said said quantity of the separated coarse particles decreases.

4. Vn the operation of a grinding mill to which a stream of Vsolid material flows for` grindingand from which the ground material is taken for separation into relatively fine and coarse particles; the method that includes projecting a o'w of air carrying a stream of the separated coarse particles in varying quantities against said stream of solid material in a directicn andat a velocity such that the kinetic energy of said particles variably restrains the flow of said solid material to the mill, thereby causing the rate at which said material is fed to the mill to decrease as the quantity of separated coarse particles being projected against said stream of material increases, and to increase as said quantity of the separated coarse particles decreases.

5. In the operation of a grinding mill to which a stream of solid material is fed for grinding and from which the ground material is taken ior separation into relatively `ine andV coarse particles; the method that includes maintaining substantial constancy vin the size of said fine particles by projecting a stream of the separated coarse particles in varying quantities downwardly and angularlyagainst a downiiowing stream of said solid material at an angle of contact therewith and at a velocity such that the changing kinetic energy of said particles causes therate at which said material is fed to the mill todecrease as the quantity ofseparated` coarseparticles being projected against said stream of material increases, and to increase as said quantity of the separated coarse particles decreases;

6. In the operation of a grinding mill to which a stream of solid material is fd'for grinding and from which the ground material is taken forY separation into relatively fine and coarse parti- I cles; the method that includes maintaining a stream of said solid material flowing by gravity to the mill .through a passage and then through an opening-of smaller size than said passage, and controlling the rate of said feed by projecting at the discharge side of said opening a stream of the separated coarse particles in varying quantities against A'said solid material flowing through the opening "atfaniangle of contact and at a velocitysuch that thefk'inetic energy of said par-,

ticles variably restrains the flow of solid material through said opening, thereby causing the rate at which said material is fed to the 'mill to decrease as the quantity of separated-'coarse particles being projected against said stream of material increases, and to increase as said quantity of the separated coarse particles decreases.

7. In the operation of a grinding mill to which a stream of solid material is fed for grinding and from which the ground material is taken for separation into relatively fine and coarse parn ticles; the method that includes maintaining a stream of said solid material flowing by gravity to the mill through a passage and then through an opening of smaller size than said passage, and controlling the rate of said feed by projecting at the discharge side of said opening a ow of air carrying a stream of the separated coarse particles in varying quantities downwardly against the stream of solid material fiowing through the opening at an angle of contact therewith and at a velocity such that the kinetic energy of said particles variably restrains the flow of said solid material to the mill, and the rate at which said material is fed tol the mill is caused to decrease as the quantity of separated coarse particles being projected against said stream of material increases, and to increase as said quantity ofthe separated coarse particles decreases.

8. In the operation of a grinding mill to which i quantity of.

a stream of solid `material is fed for grinding and from which the ground material is taken for separation into relatively fine andicoars'e particles; the method ,that includes maintaining a stream of said solid material nowing by gravity tothe mill through an opening of downwardly increasing width and of smaller size than said passage, and controlling the rate of said feed by projecting at the discharge side of said 'opening a stream of the separated coarse particlesV in varying quantities against said solid material flowing through the opening at an angle of contact and at a velocity Vsuch :that the kinetic energy,Y of said particles variably restrains Vthe iiow of solid material through said openingj'thereby causing the rate atwhich said material/is fed to the mill to-decrease'as lthe quantity of'separated coarse-particles being projectedagainst said stream of material increases, and to increase as said quantity of the separated coarse particles decreases. Y v f Y l 9. In`the operation ofa rotary grinding millI applying substantially constant grinding energy* to solid feed material being ground; the methodA that includes withdrawing the ground material from the mill and separating itffinto relaitvely fine land, coarse particles, and diiecting-together-j and then into the mill, downwardly convergentl separate streams of said solid' feed material-and varying quantities ofthe separated coarse parl' ticles, said streams converging at an angle of substantially 90 degreesand the stream of sepav rated coarse particlesbejng projected against' tlie: feed material streamat a velocity such that the? kinetic energy of sairiparticles variably restrainsV the flow of said f "d material tothe mill, and

the rate of flow/f feedmaterial into ythefmillEW increases and" decreases, respectively, as -the'l 1 ,i against the increases.

i 1Q: "The combination` comprising a grinding#- m'ill, means for feeding a stream of solid'mate-i ,."rial for grinding .in the mill, means for separat-4 ing the ground `material into relatively fine and coarse particles, and a conduit for directing a stream of varying quantities of the separated coarse particles against said stream of solid material, said conduit being positioned angularly relative to said feeding means so that the kinetic energy of said particles variably restrains the ow of said material to the mill and causes the rate at which said material is fed to the mill to decrease as the quantity of separated coarse particles being directed against said stream of material increases, and to increase as said quantity of the separated coarse particles'decreases.

11. The combination comprising a grinding mill, means for feeding by gravity a downwardly flowing stream of solid material for grinding in the mill, means for separating the ground material into relatively iine and coarse particles, and a conduit arranged to project a downwardly flowing stream of varying quantities of the separated coarse particles against said stream of solid material at an angle of contact such that the kinetic energy of theV particles Vvariably restrains th flow of said material and causes the rate at which said material is fed to the mill to decrease as the quantity of separated coarse particles being directed against said stream of material increases, and to increase as said quantity of the separated coarse particles decreases.

12. The combination comprising a rotary grinding mill, means forming a passage through separated coarse particles directed feed material stream decreasesJandj which a stream of solid material ows downwardly by gravity forl grinding in the mill, said passage containing a restricted opening through which said material ows, means for separating the ground material into relatively fine and coarse particles, and means for directing a stream of Vvarying quantities of the coarseV particles downwardly and angularlyagainst the material flowing through said opening so that the kinetic energy of the particles variably restrains the flow of said material and causes the rate at which said material is fed to the mill to decrease as the quantity of separated coarse particles being directed against'l saidstream of material increases, and to increase as said quantity of the separated coarse particles decreases. f

13. The combination comprising va rotary grinding mill, Vmeans forming a. downwardly inclined passage through which a stream of solid material flows by gravity for grinding in the mill, a vertically disposed wall in said passage containing an opening restricting the passage and through which said materialows, said opening having downwardly increasing width, means for separating the ground material into relatively fine and coarse particles and means for directing a stream of varying quantities of the coarse particles downwardly and angularly against; thematerial owing through said opening so that the kinetic energy of the particles variably restrains the now of said material and causes the rate;at which said material is fed to the mill to decrease as the quantity of separated coarse particles being directed against said stream of material increases, and to increaseas said quantity of the 5 separated coarse particles decreases.

14. The combination comprising a, grinding mill, means forming a pair of downwardly inclined passages converging to a locus of intersection communicating with said mill, means for maintaining a stream of solid feed material to be ground in a state of gravity ow downwardly through one of said passages into the mill, means for withdrawing ground material from the mill and for separating the -withdrawn materialinto relatively nne andcoarse partlclesfmeans for passing astream of varying quantities of the separated coarse particles downwardly through c the other of said passages, and means for impinging said stream of coarse particles against said stream of solid feed material at said locus of intersection of the passages so thattheikinetic energy of the particles variably restrains the flow of said material and causes the rate at which said feed material is fed to the mill to decrease as the quantity of separated coarse particles being directed against; said stream of feed material increases, and to increase as said quantity of the separatedcoarse particles decreases.

15. The combination` comprising a grinding mill, means forming a pair of\downwardly inclined passages converging to a locus of intersection communicating with said mill, means for maintaining a stream of solid feed material ,tov

be ground in a state of gravity ow downwardly through one of said passages into the mill, means for withdrawing ground material from the mill and for separating the withdrawn material -into relatively ne and coarse particles, means for passing a stream of varying quantities of the separated coarse particles downwardly through the other of said passages,'and means at said locus of intersection of the passages causing the l rate at which said feed material is fed to the mill to decrease as the quantity of separated coarse particles being directed against said stream of feed material increases, and to increase as said quantity of the separated coarse particles decreases, the last mentioned means comprising a vertically disposed wall at said locus of intersection and containing an opening/through which said feed material ows, and means for directing said stream of separated coarse particles downwardly against the material passing through said opening and at an angle such that the kinetic energy of said particles variably restrains the flow of solid material to the mill.

WILSON C. HANNA. HARRY E. KAISER. ARTHUR HARVEY. 

